Spark plug



March 24, 1931. HA RABEzzANA SPARK PLUG Filed May `5, 1928 il Truc T01 Patented Mar. 24, 1931 UNITED STATES PATENT OFFICE HECTOR RABEZZANA, F FLINT, MICHIGAN, ASSIGNOR T0 A C SPARK PLUG COMPANY, OF FLINT, MICHIGAN,` A COMPANY OF MICHIGAN SPARK PLUG Application led May 5, 1928.

This invention relates to improvements in spark plugs for internal combustion engines and is particularly adapted for use With spark plugs of the type wherein an insulator cap or dome is screw threaded into engagement with the shell and cnclcses the upper end of the insulator core surrounding a central electrode and carries a terminal connector stud electrically connected with the electrode through a tension spring. One of the diiculties heretofore encountered with this type of plug is due to the tendency of the cover cap or dome to work loose, particularly by reason of the jarring and vibration, with the result that the connection between the terminal and electrode becomes broken and permits the current to jump or arc across the break.

It is one of the objects of the present invention to overcome such trouble by the provision of a simple and economical locking arrangement for holding the cover cap against accidental looseness after assembly.

A further object is to provide a self-acting device that permits the parts to be readily assembled, but which oli'ers resistance to any tendency of the parts to move relative to each other and become loose.

Other objects and advantages will be apin connection with the accompanying drawing, in which:

Figure 1 is a vertical sectional view of a spark plug embodying the present invention.

Figure 2 is al transverse sectional view taken on line 2-v-.2 of Figure 1.

Figure 3 is a side elevation of the dome for the upper end of the spark plug with the locking means that holds it in assembled position.

Figure 4 is a bottom plan view of the parts shown in Figure 3.

Figures 5, 6 and 7 are fragmentary side elevations, partly in section. showing alternative forms of the locking means.

In the accompanying drawing. the rcterence character 1 indicates a main shell or f bushing having a hexagonal head portion 2 for the engagement of a wrench and a re- 50 duced end portion 3 carrying screw threads parent from the following specification taken Serial No. 275,379.

for engagementrwithin the customary spark plug opening in an engine cylinder block. Centrally positioned within the shell 1 is a cylindrical insulator core 4 of porcelain, quartz or other suitable non-conducting material enclosing an electrode or current conducting wire 5 which is spaced a short distance from the electrode 6 carried by the main shell to thereby form a spark gap. A retainer collar 7 having screw threaded engagement within the bore of the shell surrounds the insulator core 4 and bearsagainst the upper shoulder aliorded by the enlarged portion 8 of the core and holds the lower shoulder of lthe enlargement tightly against a sealing gasket 9 and a corresponding shoulder on the shell.

Secured to the upper end or top of the insulator core is a plate or disc 10 having contact with the central electrode 5 and against which bears a coiled tension spring 11 eX- tending into an opening on the under side of the terminal head or connector stud 12 to which a current conducting wire may be attached. The terminal connector head 12 is carrled by a dome or cap member 13 preferably molded or otherwise formed of phenolic condensation material, hard rubber, or other suitable insulating material, and which encloses and protects the upper end of the insulator core and has screw threaded engagement within the upper portion of the shell.

To lock the cap 13 against looseness or unscrewing, as may tend to occur as a result of vibration and jarring and thereby breaking the ignition circuit, provision is here made to hold the cap in place. For instance, a spring element 14 comprising a single coil of wire with one end turned upwardly as at 15 for engagement in an opening in the bottom of the cap 13 may be employed. ,The spring is initially of larger diameter than the bore of the shell, and upon being contracted and positioned therein its tendency to expand will cause it to exert its tension outwardly against the screw threads formed in the bore, thereby affording a certain degree of frictional resistance to the unthreading of the cap. The spiral course or convolution of the spring coil extends in a direction opporotation or movement to unthread the cap will have a tendency to unwind or expand the coil, which serves to augment the inherent expansive tendency of the coil, and so increase the frictional contact with the shell to resist such movement. However, the application of force as through a suitable tool or wrench will overcome this resistance and allow disassembly, should occasion require.

In lieu of the spring coil for holding t-he cap in place, the locking arrangement shownl in Figure 5 may be employed. This consists of a washer 17 interposed between the cap 18 and shell 19 and having an upwardly extending spring finger or tongue 20 for contact with one of the iat faces formed on the cap for rthe engagement of a wrench. The washer lies within a depression in the top of the shell and the spring inger extends in a radial slot or notch for holding the washer against rotation.

Fi re 6 illustrates another form of lock for t e cap, in which the top surface of the outer shell has been serrated or toothed as at 22, and a spring finger 23 carried by the cap 24 engages with the teeth as the cap is screwed into place, and then holds the cap against unscrewing.

A still further modification is shown in Figure 7 wherein a ring 25 rests upon the retainer collar 26 and has a dependent ear 27 extending into an opening in the collar and one or more upwardly extending spring arms 28 engaging with serrations or teeth 29 in the lowe'x` end of the cap 30.

It will be apparent that with eachl of the several locking arrangements shown the cap will `be held again looseness, but that when suiiicient force is exerted as by the proper manipulation of a suitable tool, the locking means will yield to permit rotation of the cap for screwing or unscrewing the same in the bore of the shell..

I claim:

1. A spark plug having an outer shelf surrounding an insulator core and a dome enclosing the top of the core and having screw threaded engagement with the shell, character1zed by a circumferentially expansible coil spring associated with the dome for direct engagement with the threadsof the shell, and having a spiral course opposite to that of the threads.

2. A spark plu having a shell, and a cover cap threaded in t e top of the shell characterized by a coil spring circumferentially expansible into engagement with the interior surface of the wall of said shell, and having :incassi one end free and the other end connected with the cap, the spiral course of the spring being opposite to that of the threads, whereby the threading or unthreading of the cap Iwill tend respectively to wind or unwind the coil.

3. A spark plug having a shell, and a cover cap threaded in the top of the shell characterized by a spring element carried by the cap and adapted for frictional contact with the threads of the shell to offer resistance to the movement of the cap in one direction.

4. In a spark plug, an insulator core enclosing an electrode, a shell surrounding the core, a cover cap enclosing the top of the core and having screw threaded engagement with the shell, a terminal connector carried by the cap in spaced relation with the electrode, a spring interposed between the connector and electrode to establish electrical connection therebetween` and means between the cap and shell to yieldingly resist separation of the cover cap from the shell.

5. The structure of claim 4, wherein said means comprises a coil spring expansible into engagement with the shell and movable with the cap and whose spiral course extends opposite that of the screw threads.

6. The structure of claim 4, wherein said means consists `of a spring element having frictional engagement with one of said parts.

7 The structure of claim 4, wherein said means consists of a spring element fixed to the cap and having frictional engagement with the shell.

8. A spark plug ofthe type wherein a cover cap of insulating material encloses the upper end of an insulator core and carries a connector terminal for electrical connection with an electrode positioned in the core, and is detachably threaded into the outer shell surrounding the core, characterized by a coil of spring wire associated with the cap for rotation therewith and expansible into engagement with the screw threads in said shell, the spiral convolution of the spring coil extending in a direction opposite to that of the screw threads, whereby the threading together of the cap and shell tends to wind the coil and the unthreading of the cap and shell tends to unwind the coil, which unwinding tendency together with the inherent expansive tendency of the spring coil, by the engagement of the coil with the shell, offers frictional resistance to the separation of the cap and shell.

9. A spark plug having a shell, and an insulator dome having screw threaded engagement with the shell, characterized by an expansible spring coil extending across the screw threads in said shell and having an angularly turned end portion engageable with the cap, whereby expansion ofthe coil against the threads rictionally resists relative movement between the cap and shell.

10. A sparkl plug of the type wherein an insulator dome has screw threaded engagement with a shell, and has a series of flat peripheral surfaces, characterized by a washer interposed between the dome and shell and provided with a spring iner engageable with said flat surfaces to yiel ingly resist separation of the dome and shell.

11. A spark' plug of the type wherein an insulator dome is removably secured to a shell, characterized by means to yieldingly resist separation of the dome and shell consisting of a springnger projecting into an opening in the dome. v

12. A spark plug of the type wherein an insulator dome has screw threaded engagement with a shell and is provided with a toothed portion, characterized by an element xed in relation with said shell and provided with a spring linger engageable with said toothed portion to yieldingly resist relative movement between the dome and shell.

In testimony whereof I alix my signature.

HECTOR RABEZZANA. 

